1. Field of Invention
The present invention relates to an expansion band, and more particularly to an expansion band with unilateral resistance and a manufacturing method thereof.
2. Description of Related Arts
Generally, an expansion band always has an inner cavity capable of being filled with air or liquid to increase its volume, which causes the expansion of the band. However, this kind of expansion is nondirectional so that this expansion band could not provide a directional expansive force, such as a longitudinal expansive force, which is widely used to force vertebras to stretch to eliminate additional pressure between vertebras.
In U.S. Pat. No. 7,618,509, Ickchun Chang disclosed a wrinkled band as illustrated in FIG. 1A and FIG. 1B. The wrinkled band comprises a first adhesion sheet 01 and a second adhesion sheet 01 overlapped with each other by an outer peripheral rim 01a and an adhesion line 012a, and an elastic band 06 disposed in the inner space 04 of the overlapped adhesion sheets and connected to the above end and the below end of the adhesion sheets 01 by a connection adhesion band 05.
Referring to FIG. 2, the elastic band 06 is stretched by the connection adhesion band 05 and the connection adhesion band 05 is further fixed onto the above below ends of a mounting die 09 to keep the elastic band 06 stretched. The adhesion sheets 01 respectively cover the top bottom surfaces of the mounting die 09 and then are pressed by a high-frequency operating die 08 to form the outer peripheral rim 01a and the adhesion line 012a, thereby the adhesion sheets 01 are overlapped with the elastic band 05 and the connection adhesion band 06 enclosed therein. The outer peripheral rim 01a forms the inner space 04 and the adhesion line 012a further divides the inner space 04 with certain regularity to form an air passage 02. As the elastic band 05 is enclosed in the overlapped adhesion sheets 01, referring to FIG. 1B, the elastic band 05 is enclosed within the air passage formed by the adhesion line 012a. 
The high-frequency operating die 08 further comprises a pressurizing means 07 to press the adhesion sheets 01 with the connection adhesion band 06 together. Hence, referring to FIG. 1B, the connection adhesion band 06 is adhered to the adhesion sheets 01 on the outer peripheral rim 01 a to fix the elastic band 05 in the air passage 02, i.e., one end of the elastic band 05 is fixed to an above end of the air passage 02 by a connection adhesion band 06 and another end the elastic band 05 is fixed to an below end the air passage 02 by a connection adhesion band 06.
As mentioned above, the elastic band 05 is disposed within the air passage 02 and is adhered to the overlapped adhesion sheets 01, when the wrinkled band relaxes, the elastic band 05 contracts to a relaxation situation to wrinkle the adhesion sheets 01 together with a smaller longitudinal length, then when air passage 02 is filled with air, the wrinkled band expands with a bigger longitudinal length and stretches the adhered elastic band 05, which further strains the adhesion sheets 01 back. That means the elastic band 05 resists the expansion of the expansion band, and the resistance of the elastic band 05 affects the expansive force on all the laterals of the wrinkled band.
As the elastic band 05 and the adhesion sheets 01 are fixed together only by the outer peripheral rim 01a, when the wrinkled band expands, the outer peripheral rim 01a not only bears the expansive force provided by the air inside, but also bears the strain force provided by the elastic band 05. Then as the outer peripheral rim 01a is formed only by heated and pressed by the high-frequency operating die 08, the outer peripheral rim 01a cannot bear these forces much, persistently and frequently. That means the outer peripheral rim 01a is very easily to be torn up by these forces, resulting that the air will leak out. Finally, the wrinkled band can not be used anymore.
Referring to FIG. 3, a body is surrounded by the wrinkled band, which is subsequently filled with air to expand, the expansive force on the surface touching the body forces the vertebras to stretch, thereby the additional pressure between the vertebras will be eliminated. However, as the elastic band 05 disposed within the air passage 02 strains all the adhesion sheets 01 back in the opposite direction, the strain force will balance a part of the expansive force. Hence, the expansive force of the wrinkled band is decreased by the resistance of the elastic band 5 and cannot be used effectively to obtain a satisfied treatment effect.
Furthermore, considering that the adhesion sheets 01 and the stretched elastic band 05 are pressed together by the high-frequency operating die 08 at the same time, it is very hard to control the pressure. If the pressure is a little smaller, the outer peripheral rim 01a will not be strong enough to bear the strain force of the elastic band 05, then the adhesion sheets 01 will be torn up to cause a waste product. Besides, the high-frequency operating die 08 is always heated to weld the adhesion sheets 01 together, and then the adhesion sheets 01 are cooled to form the outer peripheral rim 01a. However, if the heating time or the cooling time is not controlled well, a waste product will be obtained.